STRUCTURE OF ALKYLSILOXANE MONOLAYERS ON SILICON SURFACES INVESTIGATED BY EXTERNAL REFLECTION INFRARED-SPECTROSCOPY
STRUCTURE OF ALKYLSILOXANE MONOLAYERS ON SILICON SURFACES INVESTIGATED BY EXTERNAL REFLECTION INFRARED-SPECTROSCOPY
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DOI：
10.1021/la00004a043
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发表时间：
1995-04-01
期刊：
影响因子：
3.9
通讯作者：
KRISCHANITZ, A
中科院分区：
文献类型：
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作者：
HOFFMANN, H;MAYER, U;KRISCHANITZ, A
在干燥惰性气体条件下，从稀溶液中吸附制备了自组装的烷基三氯硅烷(CH3（CH2)(n)SiCl3, n = 10,13 -17）单层，并利用外反射红外光谱研究了单层膜中的烃链取向。基于光谱模拟和拟合程序的单层反射光谱定量分析表明，这些单层中的烃链向表面法线平均倾斜8度。在单层反射光谱中发现，吸附分子的烃链长度与nu（CH2）吸收强度之间存在线性关系，这进一步支持了该系列吸附化合物具有恒定链倾斜角的有序膜结构的基本守恒。然而，CH拉伸吸收的峰移和能带变宽表明，随着链长的减少，结构无序性略有增加，这归因于构象无序烃链的增加。在常压条件下制备的短链化合物（n = 10, n = 13）单层膜的膜结构发生了显著变化。薄膜由各向同性无序的液体状区域和有序的结晶区域组成。另一方面，长链化合物在大气和干燥惰性气体条件下产生相同的膜结构。
Self-assembled monolayers of homologous alkyltrichlorosilanes (CH3(CH2)(n)SiCl3, n = 10, 13-17) on bulk silicon substrates have been prepared by adsorption from dilute solutions under dry inert gas conditions and the hydrocarbon chain orientation in the monolayer films has been investigated by external reflection infrared spectroscopy. A quantitative analysis of the monolayer reflection spectra based on a spectral simulation and fit procedure reveals that the hydrocarbon chains in these monolayers are tilted by an average of 8 degrees toward the surface normal. A linear relationship was found between the hydrocarbon chain length of the adsorbate molecules and the nu(CH2) absorption intensities in the monolayer reflection spectra, which further supports an essential conservation of an ordered film structure with a constant chain tilt angle within this series of adsorbate compounds. A slight increase of structural disorder with decreasing chain length was indicated, however, by peak shifts and band broadenings of the CH stretching absorptions and has been ascribed to an increased amount of conformationally disordered hydrocarbon chains. Significant changes in the film structure were observed for monolayers of short-chain compounds (n = 10, n = 13) prepared under ambient atmospheric conditions. The films consist of isotropically disordered, liquid-like regions and ordered, crystalline domains. The long-chain compounds, on the other hand, yielded identical film structures under both atmospheric and dry inert gas conditions.